"The Heart Is Locked" tells the story of Yun Zhiyan, the daughter of the Prime Minister of the Zhou Dynasty, who disguises herself as a man and transforms into the "Mr. Miaoshou", and becomes acquainted with Xiao Jinyu, the prince of Zhenbei, through the art of mechanism. From their first encounter with each other to cooperation in disaster relief, from secret love to rescue on the battlefield, the two work together to overcome the conspiracy in the court and the war at the border. When a talented female mechanic meets the Prince of War, a battle about skill and courage, identity and sincerity slowly begins. They used ingenious mechanisms to solve the crisis, broke through the shackles with their sincere hearts, and finally concluded their lifelong vow with the original "Heart-Linking Lock".
